The number of over-60s forced to retire against their will increased dramatically last year to 100,000 as employers targeted mature workers for job cuts in the recession.

An average of just 25,000 sexagenarians had been forced out of the workplace in each of the previous two years, according to Age UK. The charity highlighted the fourfold jump as the government unveiled proposals to scrap the default retirement age of 65 and decreed employers should no longer be free to push someone out of their job because of their age.

Age UK reckons axing of the 100,000 mature employees cost the UK £3.5bn in lost economic output, and accused business organisations of trying to maintain "an unequal status quo".

"Employers are trying to breathe life into dead arguments in a desperate attempt to keep the upper hand over older workers' retirement decisions," said director Michelle Mitchell.

"The government has made the right call on forced retirement and we encourage ministers to stand by it."

Employers have argued the changes will make it hard to discuss the subject of retirement with older workers who may not be able to work so effectively as younger staff, particularly in manual jobs.

Business groups have also attacked the timetable for change – of just over a year – as too tight. But Age UK says they have already had plenty of time to find new ways to talk to older staff about their future."There must be a better way of broaching this subject than waving the threat of forced retirement at them," said Mitchell.

The government wants the law changed to keep pace with rising life expectancies and the costs entailed. Announcing the plan, last week, it published an "impact assessment" claiming the benefits outweighed the costs.

"There's overwhelming evidence that older workers, the UK economy, public finances and employers themselves will all benefit from the abolition of forced retirement," said Mitchell.